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#507043 - 05/26/04 09:30 AM Change ATF when hot or cold?
ChrisW Offline

Registered: 11/04/03
Posts: 941
Loc: Central Valley, CA
I've got some time to kill, so i thought I'd do an oil change and ATF change on a 1991 toyota previa.

Should I change the ATF when it is warm or when it is cold? If it helps, the dipstick has a cold and hot reading level.

I'm just going to do a drain and refill this time since the filter was changed about 30k ago. I will change the filter when i order it from napa or somethign.

#507044 - 05/25/04 10:16 PM Re: Change ATF when hot or cold?
Kestas Offline

Registered: 06/04/02
Posts: 11482
Loc: The Motor City
Do it hot. It makes for better draining. If you're worried about refilling it properly, you can measure the amount that's removed and match that amount with new fluid. Or just refill, leaving it a quart short. Drive around a bit and read the exact level. This'll tell you exactly how much you need to top off.

I agree with leaving the filter in this time, but consider removing the pan to clean all the silt and magnet fuzz on the bottom.

Instead of just a drain and refill, consider a complete exchange where you disconnect the return line and refill the transmission while the transmission is pumping out the old stuff with the car in idle. Though it's better than doing nothing, I never just drain and refill anymore. To me that's just like leaving the oil filter untouched during an oil change.

#507045 - 05/25/04 11:47 PM Re: Change ATF when hot or cold?
Eiron Offline

Registered: 09/25/02
Posts: 951
Loc: Loveland, Colorado
Does more fluid get "pushed out" when the tranny's hot, or does more get "trapped" in the various converters, valves & such because it hasn't had time to drain down?

[I dont know]

#507046 - 05/26/04 03:37 AM Re: Change ATF when hot or cold?
Kestas Offline

Registered: 06/04/02
Posts: 11482
Loc: The Motor City
This depends on the draining technique. If you let it drain for an hour (or better yet, overnight), the 'trapping' effect is nil. You will get more fluid out if you let it drain longer. At warm temperatures, the fluid is less viscous, plus it probably has more contaminants in suspension that'll get carried out with the fluid.

#507047 - 05/26/04 03:39 AM Re: Change ATF when hot or cold?
JohnBrowning Offline

Registered: 05/01/03
Posts: 9448
Loc: USA
Well seeing how you have a drain plug skin damage is not a consideration so drain hot if you can. You will in theory get more contaminets out with hot fluid. I prefer to measure the fluid that comes out in 1 gallon milk jugs. It makes it really easy and idiot proof to put back what came out. You will always get more out then the owners manual claims. Most Toyota will drain 1/2 to 1 quart more out then what the owners manual states. THis is why I always buy at least 1 extra quart of ATF.

#507048 - 05/29/04 09:56 AM Re: Change ATF when hot or cold?
DEWFPO Offline

Registered: 02/09/03
Posts: 264
Loc: High in the Rockies
I find hot is best. Drains faster and more solids are still in suspension. The downside is that the fluid is so damned hot to handle. So be careful.


#507049 - 05/31/04 08:43 PM Re: Change ATF when hot or cold?
Spector Offline

Registered: 06/10/02
Posts: 3348
Loc: Chattanooga, TN
I don't think it makes any difference as ATF has such a low viscocity to begin with it flows well hot or cold. I let mine drain overnight so it really make no difference to me and I have done it hot and cold, cold is slightly easier to work with.

I also measure what was taken out as this makes the refill much easier, the same amount (unlike oil in the crankcase) does not always drain out so that is why I measure before replacing.